Dia can be used to draw many different kinds of diagrams. It currently has special objects to help draw entity relationship diagrams, UML diagrams, flowcharts, network diagrams, and many other diagrams.
Unified Modeling Language Tools
Initial gradient support for Standard objects
Object upgrading like "Upgrade to Bezierline" in context menu
Optional OGDF based automatic layout plug-in
Text fitting options for Flowchart objects
Groups can be scaled and rotated
Open Source Software
Small (<50 employees), Medium (50 to 1000 employees), Enterprise (>1001 employees)
Dia by The GNOME Project is a GTK+ based diagram creation program for GNU/Linux, MacOS X, Unix, and Windows, and is released under the GPL license. It is roughly inspired by the commercial Windows program 'Visio,' though more geared towards informal diagrams for casual use.
Dia can be used to draw many different kinds of diagrams and it currently has special objects to help draw entity relationship diagrams, UML diagrams, flowcharts, network diagrams, and many other diagrams. It is also possible to add support for new shapes by writing simple XML files, using a subset of SVG to draw the shape. The program can load and save diagrams to a custom XML format (gzipped by default, to save space), it can export diagrams to a number of formats, including EPS, SVG, XFIG, WMF and PNG, and it can print diagrams (including ones that span multiple pages). It is worth noting that the program is maintained on a voluntary basis; there's no fixed plan for when what will be done, nor can The GNOME Project tell anybody to code specific parts.
Thus, the development tends to happen where people get annoyed enough with the current state that they do something about it. The GNOME Project (the maintainers) are happy to get contributions; however, they will not automatically add any patch they are sent. Nevertheless, its developers have no claim to any diagrams that users create using it. Therefore, users are free to license any diagrams they create with Dia however they wish.